Printed on in ABS on a Kossel Clear. I didn't get a photo of it before I gave it to someone, but it came out quite thin. We broke off the area between the USB port and power jack while trimming. The mounting posts were kind of a mess to clean up and we wound up cutting them off. Maybe it's worth having versions of the bottom half without the posts? The lid was slightly large but I should have thought to shrink it a couple percentage points. I did the closed bottom with no holes but that makes it quite a pain to get the board back out of the case. (That was with a Sparkfun Redboard though which I think was somewhat larger than other boards.)
I'll try another print of it sometime because I really like the design.

You can replace that with anything you want. Either take the OpenSCAD file from github and use a different DXF file or just modify the STL of the top part that has no logo with any STL editor you like.

This is almost exactly what I was looking for. The only
thing that would make this more appealing would be the additional option for
mounting holes on the bottom portion of the case. If I wanted to incorporate
the Arduino in a project, I would use the mounting holes on the case rather
than removing the Arduino from this enclosure. Thanks for sharing the files!

I printed the base w/holes and the mounting holes went the full height of the box and there were not cutouts for ports. Sturdy box, but not what is pictured, though the GCODE seems to match what I wound up with.

I don't have a duemilanove to test. As far as I know the only difference is that the duemilanove has only 3 pcb holes. There is a switch in the scad file to print only the base of the 4th pin, but I couldn't test if that fits.

The fit on this is really nice! thanks very much. My extruder needs a bit of adjusting to get a good print, but it so far so good. Seems like you could just throw arduino shields right over the top of the case since the headers are open and the fit is so good.